Solar-driven interfacial water evaporation, which concentrates solar heating at the water surface, has attracted increasing interest in pursuing highly efficient solar desalination. The rapid evaporation of water at the light absorber surface would induce a high concentration comparable with that of brine underlying the interface, which however has been paid much less attention and has never been proposed to produce electricity. Here in this work, we proved that, the theoretical real-time salinity power generated between the surface water and bulk seawater could be 12.5 W m⁻² during steam production under one sun illumination. By employing a hybrid system based on a piece of carbon nanotube modified filter paper and a commercial Nafion membrane, we achieved a maximum solar thermal efficiency of up to 75% and derived extra electricity power of ∼1 W m⁻² under one sun illumination. These results provide a novel avenue for blue energy utilization, demonstrating the potential for solar desalination and electricity generation under natural sunlight simultaneously.

Thermogalvanic cells offer a cheap, flexible and scalable route for directly converting heat into electricity. However, achieving a high output voltage and power performance simultaneously from low-grade thermal energy remains challenging. Here, we introduce strong chaotropic cations (guanidinium) and highly soluble amide derivatives (urea) into aqueous ferri/ferrocyanide ([Fe(CN)₆]⁴⁻/[Fe(CN)₆]³⁻) electrolytes to significantly boost their thermopowers. The corresponding Seebeck coefficient and temperature-insensitive power density simultaneously increase from 1.4 to 4.2 mV K⁻¹ and from 0.4 to 1.1 mW K⁻² m⁻², respectively. The results reveal that guanidinium and urea synergistically enlarge the entropy difference of the redox couple and significantly increase the Seebeck effect. As a demonstration, we design a prototype module that generates a high open-circuit voltage of 3.4 V at a small temperature difference of 18 K. This thermogalvanic cell system, which features high Seebeck coefficient and low cost, holds promise for the efficient harvest of low-grade thermal energy.